The present invention relates generally to a manner by which to effectuate power control of the power level at which a communication signal is communicated in a two-way communication system, such as a cellular communication system in which both a pilot channel signal and a traffic channel signal are transmitted. More particularly, the present invention relates to apparatus, and an associated method, by which to make power control decisions by which to power control the traffic channel signal responsive to calculation of time rates of change of values associated with signal indicia, such as the SIR (Signal to Interference Ratio), of the pilot channel communication signal. Earlier power-control decisions are made, in contrast to conventional closed-loop, power-control techniques, to facilitate operation of an embodiment of the present invention.
A communication system is formed, at a minimum, of a sending station and a receiving station which are interconnected theretogether by way of a communication channel. Information to be communicated by the sending station is communicated upon the communication channel to the receiving station. A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of information between the sending and receiving stations.
New types of communication systems have been made possible as a result of communication technologies. A radio communication system is exemplary of a type of communication system which has benefited from advancements in communication technologies. A communication channel formed between the sending and receiving stations of a radio communication system is defined upon a radio link. Because a radio link is utilized to form the communication channel, the conventional need to utilize wire-line connections between the sending and the receiving stations is obviated. Increased communication mobility is, as a result, inherent in a radio communication system in contrast to a conventional wire-line system. Because a wire-line connection is not required to be formed between the sending and receiving stations to permit the communication of information therebetween, communications are permitted at, and between, locations at which the formation of a wire-line connection would not be possible. Also, because a communication channel is formed of a radio channel, a radio communication system can generally be more economically installed, as the infrastructure costs which would otherwise be required to install a wire-line communication system are significantly reduced in a radio communication system.
A cellular communication system is exemplary of a radio communication system which has been made possible due to advancements in communication technologies. A cellular communication system advantageously provides for radio communications with mobile stations to permit telephonic communication therewith. A cellular communication system also makes relatively efficient utilization of the portion of the electromagnetic spectrum allocated thereto and upon which radio channels are defined. The relatively efficient utilization of the allocated electromagnetic spectrum is provided through the installation of a plurality spaced-apart, fixed-site transceivers installed throughout a geographical area to be encompassed by the cellular communication system. Because of the spaced-apart positioning of the fixed-site transceivers, referred to base transceiver stations (BTSs), only relatively low-power signals need to be communicated between a base transceiver station and a mobile station. That is to say, because of the positioning of the base transceiver stations, a mobile station shall be positioned in proximity to at least one of the base transceiver stations, necessitating only low-power signals to be generated to communicate a signal to, or from, a base transceiver station. And, the same communication channel can be reused at different locations throughout the cellular communication system as the low power levels of the signals permit the reuse of the same channel according to a cell re-use scheme.
Various standards have been promulgated relating to various types of cellular, as well as other, communication systems. And, various types of cellular, as well as other, communication systems have been constructed, corresponding to such standards. The IS-95 and IS-98 interim standards, promulgated by the EIA/TIA, are exemplary of standards which pertain to a cellular communication system, utilizing CDMA (code division multiple access) communication techniques. An IS2000 standard has been proposed which also utilizes CDMA communication techniques. In a CDMA communication system, a plurality of concurrently-generated communication signals are generated upon a common bandwidth. Channel differentiation is defined by the coding by which the data which is to be communicated between sending and receiving stations is encoded.
Power control of communication signals in almost any communication system is important to minimize the possibility that a communication signal might interfere with another concurrently-generated communication signal. In a CDMA communication system in which coding provides channel differentiation between concurrently-communicated signals generated upon a common bandwidth, power control is particularly important to ensure that a communication signal is not of such a great power level to prevent the detection of other concurrently-generated signals.
CDMA communication systems, such as the aforementioned IS-95, IS-98, and the proposed IS-2000 standards, set forth, amongst other things, requirements for closed-loop power control to control the power levels at which communication signals generated in such systems are communicated. And more, more generally, because of the need to control power levels of signals generated during operation of a CDMA communication system, closed-loop power control schemes are also advantageously implemented in other types of CDMA communication systems.
Generally, in a closed-loop power control scheme, a receiving station detects signals communicated thereto by a sending station. Measurements are made at the receiving station of indicia associated with the signal detected thereat. Responsive to the measurement of the indicia, a determination is made at the receiving station as to whether subsequently-generated communication signals to be communicated to the receiving station by the sending station should be increased, or decreased, in power. Indications of such determination are returned to the sending station and the power level of subsequently-generated communication signals are altered as appropriate.
In one power control scheme set forth for the IS-2000 system, forward link power control is effectuated by measuring, at the mobile station, signal indicia associated with forward-link traffic channel signals. Namely, measurements are made of frame error rates of the frames of the forward-link traffic channel signals. The frame error rate of the traffic channel signal is associated with the SIR (signal to interference ratio) of the traffic channel signal. Responsive to the measurements, a decision is made either to request an increase or to request a decrease in the power levels of the forward-link traffic channel signals. Estimation of the SIR levels of the forward-link traffic channel signals based upon these measurements, however, are susceptible to bias and variance.
Because any delay in the alteration in the power levels at which a communication signal is communicated might adversely affect communications of other communication signals, it is important effectuate power control quickly. Measurement, and subsequent determination, of communication signal indicia at a receiving stations results in some delay in the effectuation of power control in a closed-loop power control scheme.
Any manner by which to permit earlier determination of whether to alter the power levels of the communication signals to be transmitted to a receiving station would facilitate the early effectuation of power control. Also, any manner by which to effectuate power control based upon measurements which exhibit lowered levels of bias and variance would be advantageous.
It is in light of the background information related to the effectuation of power control in a communication system that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to effectuate power control of the power levels at which communication signals are communicated in a two-way communication system, such as a cellular communication system.
Through operation of an embodiment of the present invention, a manner is provided by which to make power control decisions responsive to calculation of time rates of change of values associated with signal indicia, such as the signal to interference ratio (SIR) of a communication signal communicated upon a channel which exhibits channel characteristics similar to the channel characteristics of the channel upon which the communication signal which is to be power controlled is communicated.
By calculating the time rates of change of values associated with the signal indicia of the communication signal when received at the receiving station, earlier power controlled decisions are made, thereby to permit early effectuation of power control.
In one aspect of the present of invention, measurements are made by the receiving station of signal to interference ratios of a communication signal transmitted thereto by the sending station. In a communication system which utilizes both pilot signals and traffic signals, for instance, the signal to interference ratio of the pilot signal is first determined at the receiving station. The pilot signal is of a relatively high power level and is of a constant characteristic in the absence of fading. Differences between the measured signal to interference ratio and a target value, such as a target signal to interference ratio, are determined. If the value of the difference, so-determined, is beyond a selected range of different values, a determination is made as to whether to generate a power up command or to generate a power down command. That is to say, when the difference is greater than a selected value, the generation of a power down command is selected and, when the difference is less than another threshold value, selection of generation of a power up command is made.
In another aspect of the present invention, determination of the signal to interference ratio of a communication signal detected at the receiving station is again made. Again, the communication signal upon which the measured value of the signal to interference ratio is determined is formed of a pilot signal sent by the sending station. Differences made between measured signal to interference ratio and a target value, such as a target signal to interference ratio, are determined. If the difference is within a selected range of values, the time-rate of change of the difference is then calculated. If the time rate of change of the difference is a positive value. Selection is made to generate a power down command. And, if the time-rate of change of the difference is a negative value, selection is made to generate a power up command.
As the pilot channel signal, in the absence of fading, exhibits constant characteristics, changes in the signal are indicative of fading on the channel upon which the pilot channel is communicated. And, as the pilot and traffic channels extending between the BTS and the mobile station exhibit similar characteristics, changes in the pilot channel signal are also indicative of fading on the traffic channel. When increased fading is exhibited upon the traffic channel, the power level of the traffic channel signal must be increased to compensate for the increased fading. So, by calculating the time rate of change of the pilot channel signal, an early determination can be made of power level changes to be requested of the traffic channel signal power levels. When the time rate of change is determined to be of a positive value, a power down command is generated as the pilot channel signal, when detected at the mobile station, appears to be increasing in value, the fading is lessening. And, when the time rate of change is determined to be of a negative value, a power up command is generated. As the pilot channel signal, when detected at the mobile station, appears to be decreasing in value, the fading is worsening.
In one implementation, an embodiment of the present invention is utilized to effectuate power control in a cellular communication system, such as a cellular communication system proposed pursuant to the IS-2000 standard which utilizes CDMA communication techniques. A base transceiver station generates and transmits a pilot signal which is detected by a mobile station. The signal to interference ratio of the pilot signal is calculated. Measurements are made of the pilot signal as the pilot signal is generally of a relatively high power level and is of constant characteristics. Therefore, typically, the pilot signal level is a reliable measure of channel impairments, such as the fading to be expected upon the traffic channel. Difference calculations are performed upon the measured signal to interference ratio and a target value. If the difference value is less than a lower threshold, selection is made to generate a power up command, if the difference is greater than an upper threshold, a selection is made to generate a power down command. And, if the differences between the lower and upper thresholds are between the lower and upper thresholds, a time rate of change of the difference is calculated. If the time rate of change is a positive value, selection is made to generate a power down command. And if the time rate of change of the difference is a negative value, selection is made to generate a power up command.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a communication system in which communication signals are communicated between a first communication station and a second communication station. Regulation of power levels of a forward-link of power-controlled communication signal communicated by the first communication station to the second communication station is facilitated. A difference calculator is coupled to receive an indication of a signal indicia associated with a non power-controlled forward link communication signal. The signal indicia is representative of content detectability of the non power-controlled communication signal. The difference calculator calculates the difference between a value of the signal indicia and a selected value. A change rate calculator is coupled to the difference calculator. The change rate calculator calculates a time rate of change of differences calculated by the difference calculator when the difference is within a selected range. A power command generator is at least selectively operable responsive to the time rate of change calculated by the change rate calculator. The power command generator generates a command to command the first communication station, to alter the power levels of the forward link power-controlled communication signal.
A more complete appreciation of the present invention and to the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently preferred embodiments of the invention, and the appended claims.